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We investigated whether single nucleotide polymorphisms (SNPs) within genes encoding the alpha-1 chain of type I (COL1A1, rs2249492; rs1800012), type II (COL2A1, rs2070739) and type V (COL5A1, rs12722) collagen were associated with the... more
We investigated whether single nucleotide polymorphisms (SNPs) within genes encoding the alpha-1 chain of type I (COL1A1, rs2249492; rs1800012), type II (COL2A1, rs2070739) and type V (COL5A1, rs12722) collagen were associated with the variable response to exercise-induced muscle damage (EIMD). Knee extensor muscle strength and soreness were assessed pre-, post-, and 48h post-EIMD (120 maximal eccentric knee extensor contractions) in 65 young healthy participants, who were genotyped for the aforementioned SNPs. We found that COL1A1 (minor) T-allele carriers (rs1800012) and (major) T-allele homozygotes (rs2249492) were generally weaker (p{less than or equal to}0.019); and (minor) A-allele carriers of COL2A1 (p=0.002) and (major) T-allele carriers of COL5A1 (p=0.004) SNPs reported greater muscle soreness, all compared to their respective major (rs1800012; rs2070739) and minor (rs2249492; rs12722) allele homozygote counterparts. To conclude, the risk alleles of these four SNPs appear t...
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Different modes of perturbations have been used to understand how individuals negotiate irregular surfaces, with a general notion that increased locomotion variability induces a positive training stimulus. Individuals tend to walk slower... more
Different modes of perturbations have been used to understand how individuals negotiate irregular surfaces, with a general notion that increased locomotion variability induces a positive training stimulus. Individuals tend to walk slower when initially exposed to such locomotion tasks, potentially influencing the magnitude and variability of biomechanical parameters. This study investigated theeffects of gait speed on lower extremity biomechanics when walking on an irregular (IS) and regular surface (RS). Twenty physically active males walked on a RS and IS at three different speeds (4 km/h, 5 km/h, 6 km/h). Lower extremity kinematics (300 Hz) and surface electromyography (3000 Hz) were recorded during the first 90 s of gait. Two-factor repeated measures ANOVA was used to determine surface and speed effects (p < 0.05). Gait speed influences walking biomechanics (kinematic and muscle activity parameters) the same irrespective of surface condition. As walking speed increased, sagit...
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It remains to be determined whether running training influences the amplitude of lower limb muscle activations before and during the first half of stance and whether such changes are associated with joint stiffness regulation and usage of... more
It remains to be determined whether running training influences the amplitude of lower limb muscle activations before and during the first half of stance and whether such changes are associated with joint stiffness regulation and usage of stored energy from tendons. Therefore, the aim of this study was to investigate neuromuscular and movement adaptations before and during landing in response to running training across a range of speeds. Two groups of high mileage (HM; >45 km/wk, n = 13) and low mileage (LM; <15 km/wk, n = 13) runners ran at four speeds (2.5–5.5 m/s) while lower limb mechanics and electromyography of the thigh muscles were collected. There were few differences in prelanding activation levels, but HM runners displayed lower activations of the rectus femoris, vastus medialis, and semitendinosus muscles postlanding, and these differences increased with running speed. HM runners also demonstrated higher initial knee stiffness during the impact phase compared with ...
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Prolonged unaccustomed exercise involving muscle lengthening (eccentric) actions can result in ultrastructural muscle disruption, impaired excitation-contraction coupling, inflammation and muscle protein degradation. This process is... more
Prolonged unaccustomed exercise involving muscle lengthening (eccentric) actions can result in ultrastructural muscle disruption, impaired excitation-contraction coupling, inflammation and muscle protein degradation. This process is associated with delayed onset muscle soreness and is referred to as exercise-induced muscle damage. Although a certain amount of muscle damage may be necessary for adaptation to occur, excessive damage or inadequate recovery from exercise-induced muscle damage can increase injury risk, particularly in older individuals, who experience more damage and require longer to recover from muscle damaging exercise than younger adults. Furthermore, it is apparent that inter-individual variation exists in the response to exercise-induced muscle damage, and there is evidence that genetic variability may play a key role. Although this area of research is in its infancy, certain gene variations, or polymorphisms have been associated with exercise-induced muscle damage...
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Unstable shoes (US) continually perturb gait which can train the lower limb musculature, but muscle co-contraction and potential joint stiffness strategies are not well understood. A shoe with a randomly perturbing midsole (IM) may... more
Unstable shoes (US) continually perturb gait which can train the lower limb musculature, but muscle co-contraction and potential joint stiffness strategies are not well understood. A shoe with a randomly perturbing midsole (IM) may enhance these adaptations. This study compares ankle and knee joint stiffness, and ankle muscle co-contraction during walking and running in US, IM and a control shoe in 18 healthy females. Ground reaction forces, three-dimensional kinematics and electromyography of the gastrocnemius medialis and tibialis anterior were recorded. Stiffness was calculated during loading and propulsion, derived from the sagittal joint angle-moment curves. Ankle co-contraction was analysed during pre-activation and stiffness phases. Ankle stiffness reduced and knee stiffness increased during loading in IM and US whilst walking (ankle, knee: p=0.008, 0.005) and running (p<0.001; p=0.002). During propulsion, the opposite joint stiffness re-organisation was found in IM whilst...
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The purpose of this study was to determine whether real-time feedback (RTF) training would reduce impact loading variables previously linked with tibial stress fracture risk and whether these adaptations would influence running economy.... more
The purpose of this study was to determine whether real-time feedback (RTF) training would reduce impact loading variables previously linked with tibial stress fracture risk and whether these adaptations would influence running economy. Twenty-two male runners were randomly assigned to RTF (n = 12) and control (n = 10) groups. The RTF group received feedback based on their peak tibial axial accelerations (PTA) during six 20-min treadmill runs for 3 wk, whereas the control group adhered to the same training but without feedback. Unilateral three-dimensional kinematic and kinetic analysis and running economy measurements were conducted before, after, and at 1 month posttraining. The RTF group had significant reductions (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.01) in PTA and average and instantaneous vertical force loading rates after training as compared with no changes in the control group. These modifications in impact loads were only maintained in PTA 1 month after the training. A significant increase (P = 0.0033) in ankle plantarflexion at initial contact and a significant change (P = 0.030) in foot strike pattern from a rearfoot to midfoot strike pattern and a significant decrease (P = 0.008) in heel vertical velocity at initial contact appeared to be the primary mechanical strategies adopted by runners to reduce impact loading after RTF training. Despite these gait adaptations, running economy was unaffected. The results of this study suggest that gait retraining using RTF is an effective means of eliciting reductions in impact loading without negatively affecting running economy. However, with loading rate reductions not being maintained 1 month posttraining, further research is required to determine how these reductions in impact severity can be retained long term.
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Abstract The mechanics of cutting movements have been investigated extensively, but few studies have considered the rapid deceleration phase prior to turning which has been linked to muscle damage. This study used accelerometry to examine... more
Abstract The mechanics of cutting movements have been investigated extensively, but few studies have considered the rapid deceleration phase prior to turning which has been linked to muscle damage. This study used accelerometry to examine the influence of turning intensity on the last three steps of a severe turn. Ten soccer players performed 135° &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;V&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; cuts at five different intensities. Resultant decelerations were recorded from a trunk-mounted tri-axial accelerometer. Lower limb kinematics and ground reaction forces (GRF) from the pivot foot-ground contact (FGC) were also monitored. Average peak trunk decelerations were larger at the two preceding steps (4.37 ± 0.12 g and 4.58 ± 0.11 g) compared to the PIVOT step (4.10 ± 0.09 g). Larger peak joint flexion angular velocities were observed at PRE step (ankle: 367 ± 192 deg.s(-1); knee 493 ± 252 deg.s(-1)) compared to PIVOT step (ankle 255 ± 183 deg.s(-1); knee 377 ± 229 deg.s(-1)). Turn intensity did not influence peak GRF at PIVOT step. This study highlights the importance of steps prior to turning and their high-frequency loading characteristics. It is suggested that investigations of lower limb loading during turning should include this deceleration phase and not focus solely on pivot FGC.
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Overuse injuries to the lower extremity have often been connected with the repetitive loading of the foot and in particular its ability to absorb shock. The shock absorbing ability of the foot is thought to relate to its structure,... more
Overuse injuries to the lower extremity have often been connected with the repetitive loading of the foot and in particular its ability to absorb shock. The shock absorbing ability of the foot is thought to relate to its structure, particularly the height of the medial longitudinal arch. The purpose of this study was to investigate the shock absorption characteristics of the foot in forefoot running as measured by the dynamic load rate of the vertical ground reaction forces during the early stages of ground contact and to relate these characteristics to the height of the medial longitudinal arch. Eighteen normal athletic adult volunteers were used as subjects and all had clinically normal feet. An Arch Index was computed from lateral radiographs taken with the foot in a full weightbearing position. Dynamic load rate was computed as the first differential of the vertical force as measured by a Kistler force platform. Each subject performed ten trials of running at a speed of 3 m.s-1 ...
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Abstract The mechanics of cutting movements have been investigated extensively, but few studies have considered the rapid deceleration phase prior to turning which has been linked to muscle damage. This study used accelerometry to examine... more
Abstract The mechanics of cutting movements have been investigated extensively, but few studies have considered the rapid deceleration phase prior to turning which has been linked to muscle damage. This study used accelerometry to examine the influence of turning intensity on the last three steps of a severe turn. Ten soccer players performed 135° &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;V&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; cuts at five different intensities. Resultant decelerations were recorded from a trunk-mounted tri-axial accelerometer. Lower limb kinematics and ground reaction forces (GRF) from the pivot foot-ground contact (FGC) were also monitored. Average peak trunk decelerations were larger at the two preceding steps (4.37 ± 0.12 g and 4.58 ± 0.11 g) compared to the PIVOT step (4.10 ± 0.09 g). Larger peak joint flexion angular velocities were observed at PRE step (ankle: 367 ± 192 deg.s(-1); knee 493 ± 252 deg.s(-1)) compared to PIVOT step (ankle 255 ± 183 deg.s(-1); knee 377 ± 229 deg.s(-1)). Turn intensity did not influence peak GRF at PIVOT step. This study highlights the importance of steps prior to turning and their high-frequency loading characteristics. It is suggested that investigations of lower limb loading during turning should include this deceleration phase and not focus solely on pivot FGC.
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The metatarsophalangeal joint is an important contributor to lower limb energetics during sprint running. This study compared the kinematics, kinetics and energetics of the metatarsophalangeal joint during sprinting barefoot and wearing... more
The metatarsophalangeal joint is an important contributor to lower limb energetics during sprint running. This study compared the kinematics, kinetics and energetics of the metatarsophalangeal joint during sprinting barefoot and wearing standardized sprint spikes. The aim of this investigation was to determine whether standard sprinting footwear alters the natural motion and function of the metatarsophalangeal joint exhibited during barefoot sprint running. Eight trained sprinters performed maximal sprints along a runway, four sprints in each condition. Three-dimensional high-speed (1000 Hz) kinematic and kinetic data were collected at the 20 m point. Joint angle, angular velocity, moment, power and energy were calculated for the metatarsophalangeal joint. Sprint spikes significantly increase sprinting velocity (0.3 m/s average increase), yet limit the range of motion about the metatarsophalangeal joint (17.9% average reduction) and reduce peak dorsiflexion velocity (25.5% average r...
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The purpose of this study was to investigate the acute effects of progressive fatigue on the parameters of running mechanics previously associated with tibial stress fracture risk. Twenty-one trained male distance runners performed three... more
The purpose of this study was to investigate the acute effects of progressive fatigue on the parameters of running mechanics previously associated with tibial stress fracture risk. Twenty-one trained male distance runners performed three sets (Pre, Mid, and Post) of six overground running trials at 4.5 m.s(-1) (± 5%). Kinematic and kinetic data were collected during each trial using a 12-camera motion capture system, force platform, and head and leg accelerometers. Between tests, each runner ran on a treadmill for 20 min at their corresponding lactate threshold (LT) speed. Perceived exertion levels (RPE) were recorded at the third and last minute of each treadmill run. RPE scores increased from 11.8 ± 1.3 to 14.4 ± 1.5 at the end of the first LT run and then further to 17.4 ± 1.6 by the end of the second LT run. Peak rearfoot eversion, peak axial head acceleration, peak free moment and vertical force loading rates were shown to increase (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.05) with moderate-large effect sizes during the progression from Pre to Post tests, although vertical impact peak and peak axial tibial acceleration were not significantly affected by the high-intensity running bouts. Previously identified risk factors for impact-related injuries (such as tibial stress fracture) are modified with fatigue. Because fatigue is associated with a reduced tolerance for impact, these findings lend support to the importance of those measures to identify individuals at risk of injury from lower limb impact loading during running.
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The purpose of this study was to determine whether real-time feedback (RTF) training would reduce impact loading variables previously linked with tibial stress fracture risk and whether these adaptations would influence running economy.... more
The purpose of this study was to determine whether real-time feedback (RTF) training would reduce impact loading variables previously linked with tibial stress fracture risk and whether these adaptations would influence running economy. Twenty-two male runners were randomly assigned to RTF (n = 12) and control (n = 10) groups. The RTF group received feedback based on their peak tibial axial accelerations (PTA) during six 20-min treadmill runs for 3 wk, whereas the control group adhered to the same training but without feedback. Unilateral three-dimensional kinematic and kinetic analysis and running economy measurements were conducted before, after, and at 1 month posttraining. The RTF group had significant reductions (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.01) in PTA and average and instantaneous vertical force loading rates after training as compared with no changes in the control group. These modifications in impact loads were only maintained in PTA 1 month after the training. A significant increase (P = 0.0033) in ankle plantarflexion at initial contact and a significant change (P = 0.030) in foot strike pattern from a rearfoot to midfoot strike pattern and a significant decrease (P = 0.008) in heel vertical velocity at initial contact appeared to be the primary mechanical strategies adopted by runners to reduce impact loading after RTF training. Despite these gait adaptations, running economy was unaffected. The results of this study suggest that gait retraining using RTF is an effective means of eliciting reductions in impact loading without negatively affecting running economy. However, with loading rate reductions not being maintained 1 month posttraining, further research is required to determine how these reductions in impact severity can be retained long term.
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Young females with mild hallux valgus (HV) have been identified as having an increased risk of first ray deformation. Little is known, however, about the biomechanical changes that might contribute to this increased risk. The purpose of... more
Young females with mild hallux valgus (HV) have been identified as having an increased risk of first ray deformation. Little is known, however, about the biomechanical changes that might contribute to this increased risk. The purpose of this study was to compare kinetics changes during walking for mild HV subjects with high-heel-height shoes. Twelve female subjects (six with mild HV and six controls) participated in this study with heel height varying from 0 cm (barefoot) to 4.5 cm. Compared to healthy controls, patients had significantly higher peak pressure on the big toe area during barefoot walking. When the heel height increased, loading was transferred to medial side of the forefoot, and the big toe area suffered more impact compared to barefoot in mild HV. This study also demonstrated that the center of pressure (COP) inclines to medial side alteration after high-heeled shoes wearing. These findings indicate that mild HV people should be discouraged from wearing high-heeled s...
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The purpose of this study was to compare kinematics and kinetics during walking for healthy subjects using unstable shoes with different designs. Ten subjects participated in this study, and foot biomechanical data during walking were... more
The purpose of this study was to compare kinematics and kinetics during walking for healthy subjects using unstable shoes with different designs. Ten subjects participated in this study, and foot biomechanical data during walking were quantified using motion analysis system and a force plate. Data were collected for unstable shoes condition after accommodation period of one week. With soft material added in the heel region, the peak impact force was effectively reduced when compared among similar shapes. In addition, the soft material added in the rocker bottom showed more to be in dorsiflexed position during the initial stance. The shoe with three rocker curves design reduced the contact area in the heel strike, which may result in increasing human body forward speed. Further studies shall be carried out after adapting to long periods of wearing unstable shoes.
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ABSTRACT Purpose: Player–surface interaction is a key factor for soccer performance and the loads experienced by the human body in soccer. Thereby, the outsoles of soccer boots play an influencing role on traction properties. In this... more
ABSTRACT Purpose: Player–surface interaction is a key factor for soccer performance and the loads experienced by the human body in soccer. Thereby, the outsoles of soccer boots play an influencing role on traction properties. In this study, the influence of sole stud configuration on lower extremity kinematics and kinetics during a turning movement was investigated.Methods: Fifteen experienced soccer players performed five repetitive trials in four different sole configurations: soccer boot with removed studs, artificial turf design, firm ground and soft ground natural grass design. Subjects performed a 135° turning movement as quickly as possible in a laboratory environment. Lower leg kinematics and kinetics were collected by a motion analysis system and two force plates. Repeated measures ANOVA and post-hoc tests were used to discriminate between shoe conditions (P &lt; 0.05).Results: Movement patterns of subjects were influenced by sole configurations. The soccer boot with removed studs provoked a more vertical alignment of the shank at touchdown accompanied by lower ankle and knee joint moments in the stance phase. The soft ground design showed decreased foot translation in combination with increased ankle moments compared to the other studded boot conditions.Conclusion: Movement adaptations were primarily found in the distal part of the lower extremities. The soccer boot with removed studs increased the risk of slipping whereas the soft ground sole configuration induced relatively high loads acting on the player.
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To reduce the risk of injury associated with foot-ground interaction during sporting activities, there is a need for adequate assessment of the protective function of sports footwear. The present objectives are to review the typical... more
To reduce the risk of injury associated with foot-ground interaction during sporting activities, there is a need for adequate assessment of the protective function of sports footwear. The present objectives are to review the typical biomechanical approaches used to identify protection offered by sports footwear during dynamic activities and to outline some of the recent methodological approaches aimed at improving this characterization. Attention is focused on biomechanical techniques that have been shown to best differentiate safety features of footwear. It was determined that subject tests would be used in combination with standard mechanical techniques to evaluate footwear protection. Impact attenuation characteristics of footwear during sporting activities were most distinguished by analysis of tibial shock signals in the frequency and joint time-frequency domains. It has been argued that lateral stability and traction properties of footwear are better assessed using game-like manoeuvres of subjects on the actual sporting surface. Furthermore, the ability of such tests to discriminate between shoes has been improved through methods aimed at reducing or accounting for variability in individual execution of dynamic manoeuvres. Advances in tools allowing measurement of dynamic foot function inside the shoe also aid our assessment of shoe protective performance. In combination, these newer approaches should provide more information for the design of safer sports footwear.
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The human heel pad is a complex biological structure consisting of the fat pad and the skin. The mechanical properties of the skin layer are of significant importance to the load-bearing function of the heel pad and human locomotion. The... more
The human heel pad is a complex biological structure consisting of the fat pad and the skin. The mechanical properties of the skin layer are of significant importance to the load-bearing function of the heel pad and human locomotion. The condition of the heel skin is also directly associated with some medical conditions such as heel ulcers that may become a site for the skin breakdown, which is the most common precursor to lower extremity amputation among persons with diabetes. It is essential to develop a detailed understanding of the properties of the heel skin layer and its effect on hind foot biomechanics during heel strike. This work aims to gain a better insight into the biomechanical behaviour of the heel skin layer through a combined experimental and numerical study. The main objective is to characterise the biomechanical responses of the hind foot system during heel strike with potential variation of the skin stiffness based on a subject-specific finite element (FE) model and biomechanical testing. A three-dimensional (3D) FE model of the human hind foot incorporating a separate heel skin layer was developed based on subject-specific medical images. An inverse FE analysis of the in vivo indentation test was carried out to study the nonlinear material property of the heel skin. The FE model was then used to study the deformation of the hind foot during heel strike in comparison with the plantar pressure measurement results and to establish the effects of stiffness of the heel skin on the stress and pressure distributions. The FE foot model with subject-specific heel skin properties was successfully used to predict the deformation of the hind foot during heel strike, and the results showed good agreements with biomechanical pressure measurements. The results showed that the high pressure and stress in the heel skin appeared in the centre region during a heel strike. Heel skin stiffness sensitivity studies showed that an increase in the skin stiffness had a limited effect on the stress and contact pressure of the hind foot bones, but caused a slight increase in the skin stresses, while skin softening caused a decrease in the peak plantar pressure and its distribution pattern changed. In addition, the results also suggest that skin softening may cause a higher stress level in the bones and ligaments. The nonlinear parameter of the heel skin has been successfully predicted from in vivo indentation tests based on a subject-specific FE model. Skin properties&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; sensitivity tests clearly showed that the stiffness of the heel skin could have a direct effect on the biomechanics of the hind foot. The results suggest that individuals with a pathologically stiffened heel skin could exert an increase in the heel pressure, which may potentially lead to skin breakdown or ulcer.
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This report presents results of tests performed in neutral buoyancy by two pressure-suited test subjects to simulate Extravehicular Activity (EVA) tasks associated with the on-orbit construction and repair of a precision reflector... more
This report presents results of tests performed in neutral buoyancy by two pressure-suited test subjects to simulate Extravehicular Activity (EVA) tasks associated with the on-orbit construction and repair of a precision reflector spacecraft. Two complete neutral buoyancy assemblies of the test article (tetrahedral truss with three attached reflector panels) were performed. Truss joint hardware, two different panel attachment hardware concepts,
Book description: Simulating Change explores the history, the state of the art, and the controversies in the use of computer simulation in archaeology. Thanks to contributions from archaeological simulation pioneers such as Martin Wobst,... more
Book description: Simulating Change explores the history, the state of the art, and the controversies in the use of computer simulation in archaeology. Thanks to contributions from archaeological simulation pioneers such as Martin Wobst, the work of established veterans of the field like Mark Aldenderfer and the work of innovative young scholars like Luke Premo, this collection addresses some of the main theoretical issues in archaeological simulation. It leads the reader through a reflection on the use of simulation and presents some cutting-edge applications. Far from the usual collection of case studies, Simulating Change focuses on the history, theory, and challenges of computer simulation as told by the main protagonists. The volume will be required reading for anyone interested in how computer simulation affects the investigation of past human societies.
The use of an elastic memory composite member (EMC) as the active element in deployable optical instruments has tremendous potential. Elastic memory composite mechanisms can remove the need for mechanical latches and remove the post... more
The use of an elastic memory composite member (EMC) as the active element in deployable optical instruments has tremendous potential. Elastic memory composite mechanisms can remove the need for mechanical latches and remove the post deployed microdynamic instabilities associated with them while providing a low shock, controlled deployment. Additionally, elastic memory composite mechanisms are lightweight, simple, and have a very low coefficient of thermal expansion, which are also desirable properties for deployable optical systems. This paper describes an effort that has been done to explore this possibility. A mechanical latching actuator in an existing precision deployable optical testbed was replaced by an EMC self-locking actuator. Feasibility was assessed through a detailed design and fabrication exercise followed by experimental evaluation of a prototype actuator system in the ground-based deployable optics testbed.
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Elastic memory composite (EMC) materials exhibit many favorable qualities for deployable structures and have piqued a broad interest within America&#39;s deployable space structures industry. EMC materials are similar to traditional... more
Elastic memory composite (EMC) materials exhibit many favorable qualities for deployable structures and have piqued a broad interest within America&#39;s deployable space structures industry. EMC materials are similar to traditional fiber-reinforced composites except for the use of a thermoset shape memory resin that enables much higher packaging strains than traditional composites without damage to the fibers or the resin. This
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This paper summarizes recent results in a cooperative research program between the University of Colorado and NASA Langley Research Center in the deployment of precise antennas and reflectors from compact spacecraft. Advances in concepts,... more
This paper summarizes recent results in a cooperative research program between the University of Colorado and NASA Langley Research Center in the deployment of precise antennas and reflectors from compact spacecraft. Advances in concepts, joints, materials, ground-test methodology, and micro-structural mechanics are presented which demonstrate the potential for passively positioning deployed components to within a few microns of their desired
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Results are presented from a ground test program of an alternate mobile transporter (MT) concept and extravehicular activity (EVA) assembly procedure for the Space Station Freedom (SSF) truss keel. A three-bay orthogonal tetrahedral truss... more
Results are presented from a ground test program of an alternate mobile transporter (MT) concept and extravehicular activity (EVA) assembly procedure for the Space Station Freedom (SSF) truss keel. A three-bay orthogonal tetrahedral truss beam consisting of 44 2-in-diameter struts and 16 nodes was assembled repeatedly in neutral buoyancy by pairs of pressure-suited test subjects working from astronaut positioning devices
The use of smart materials and multifunctional components has the potential to provide enhanced performance, improved economics, and reduced safety concerns for applications ranging from outer space to subterranean. Elastic Memory... more
The use of smart materials and multifunctional components has the potential to provide enhanced performance, improved economics, and reduced safety concerns for applications ranging from outer space to subterranean. Elastic Memory Composite (EMC) materials, based on ...
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Running technique and economy (VO2submax) were examined before and after a 6-wk period of running training. Fifteen males were filmed and performed 10-min economy runs at 3.36 m.s-1 on a treadmill. An incremental treadmill test was used... more
Running technique and economy (VO2submax) were examined before and after a 6-wk period of running training. Fifteen males were filmed and performed 10-min economy runs at 3.36 m.s-1 on a treadmill. An incremental treadmill test was used to record running performance and maximal oxygen consumption (VO2max). Subjects were randomly assigned to a training group and a control group that did not participate in any running program. There were no significant changes in kinematic variables between pre- and post-training tests for either group. Neither were there any significant physiological changes over the 6 wk in the control group. However, the training group demonstrated a significantly (P &lt; 0.01) increased VO2max (57.7 +/- 6.2 vs 61.3 +/- 6.3 ml.kg-1.min-1) and running performance. VO2submax in the training group was significantly (P &lt; 0.05) worse (41.0 +/- 4.5 vs 42.4 +/- 4.3 ml.kg-1.min-1) post-training, although the percent utilization of VO2max (71.6 +/- 7.9 vs 69.3 +/- 6.9%) and submaximal heart rate (169 +/- 15 vs 161 +/- 15 beats.min-1) were significantly lower (P &lt; 0.05). The training-induced improvements in running performance could be attributed to physiological rather than biomechanical modifications. There were no changes in biomechanical descriptors of running style that signaled changes in running economy.
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The purpose of this study was to capture the lower limb kinematics before during and after ball impact of soccer kicking by examining the influence of both sampling rate and smoothing procedures. Nine male soccer players performed maximal... more
The purpose of this study was to capture the lower limb kinematics before during and after ball impact of soccer kicking by examining the influence of both sampling rate and smoothing procedures. Nine male soccer players performed maximal instep kicks and the three-dimensional leg movements were captured at 1000 Hz. Angular and linear velocities and accelerations were determined using four different processing approaches: processed using a modified version of a time-frequency filtering algorithm (WGN), smoothed by a second-order low-pass Butterworth filter at 200 Hz cut-off (BWF), re-sampled at 250 Hz without smoothing (RSR) and re-sampled at 250 Hz but filtered by the same Butterworth filter at 10 Hz cut-off (RSF). The WGN approach appeared to establish representative kinematics, whereas the other procedures failed to remove noisy oscillation from the baseline of signal (BWF), lost the peaks of rapid changes (RSR) or produced totally distorted movement patterns (RSF). The results indicate that the procedures used by some previous studies may have been insufficient to adequately capture the lower limb motion near ball impact. We propose a new time-frequency filtering technique as a better way to smooth data whose frequency content varies dramatically.